Method of delivering a diffuse duty cycle

Abstract

A method for controlling the duty cycle of a pulse width modulated (PWM) output signal applied to a field winding of an alternator of a motor vehicle. The PWM signal is generated from a controller associated with a vehicle engine to control the output current from a vehicle alternator during engine operation. The method involves determining a desired duty cycle for the PWM signal to be applied to the field winding of the alternator. The method then involves determining the PWM signal's "ON" and "OFF" pattern to deliver the desired duty cycle. This is accomplished by adding the value corresponding to the desired duty cycle to a running sum value. The PWM signal to the alternator is turned "ON" if the new running sum value exceeds or is equal to 100. One-hundred is then subtracted from the running sum value before it is stored. However, if the new running sum value is less than 100, then the PWM signal is turned "OFF" and the new running sum value is then stored without subtracting 100. On the next cycle, the desired duty cycle is again added to the presently stored running sum value to produce a new value which is again checked to determine if it is greater than or equal to 100, and the above steps are repeated. The method provides better control over the duty cycle of the PWM signal which contributes to a more steady-state output of the alternator and better response to brief electrical impulses experienced by the alternator as a result of activation of various electrical subsystems of a vehicle at low engine idle speeds.

I claim: 
     
       1. A method for controlling operation of an alternator by controlling a duty cycle of a pulse width modulated (PWM) signal applied to the alternator, wherein the signal is applied by controllably turning "ON" and "OFF" a port of a controller operably associated with said alternator, said method comprising the steps of: a) setting a running sum value to zero;   b) defining a time interval;   c) determining a desired duty cycle value for said PWM signal needed to be applied to said alternator;   d) adding said desired duty cycle to said running sum value;   e) determining if said running sum value is less than a predetermined value and, if so, then causing said controller to turn "OFF" said port to thereby interrupt said signal to said alternator for said time interval;   f) determining if said running sum value is greater than or equal to said predetermined value and, if so, then causing said controller to turn "ON" said port to thereby apply said signal to said alternator for said time interval and subtracting said predetermined value from said running sum value; and   g) after the expiration of said time interval, repeating steps d), e) and f).   
     
     
       2. The method of claim 1, wherein step e) further comprises the step of defining said predetermined value as a value of 100. 
     
     
       3. The method of claim 1, wherein step f) further comprises the step of determining if said running sum is greater than or equal to said predetermined value. 
     
     
       4. The method of claim 3, further comprising the step of defining said predetermined value as a value of 100. 
     
     
       5. The method of claim 1, further comprising the step of defining said time interval to be between about one and five milliseconds. 
     
     
       6. A method for controlling operation of an alternator by controlling a duty cycle of a pulse width modulated signal applied to the alternator, wherein the signal is applied by controllably turning "ON" and "OFF" a port of a controller operably associated with said alternator, said method comprising the steps of: a) setting a running sum value to zero;   b) defining a time interval;   c) determining a desired duty cycle value for said pulse width modulated signal needed to be applied to said alternator;   d) adding said desired duty cycle value to said running sum value;   e) if said running sum value is less than 100, then causing said controller to turn "OFF" said port to thereby interrupt said signal to said alternator for said time interval;   f) if said running sum value is greater than or equal to 100, then causing said controller to turn "ON" said port to thereby apply said signal to said alternator for said time interval, and subtracting 100 from said running sum value;   g) after the expiration of said time interval, repeating steps d) and e) and f).   
     
     
       7. The method of claim 6, wherein the step of determining if said running sum value is less than 100 comprises the step of determining if said running sum value is equal to or greater than 100. 
     
     
       8. The method of claim 6, wherein said step of defining a time interval comprises the step of defining a time interval within a range of about 1 ms-5 ms. 
     
     
       9. The method of claim 6, further comprising the step of modifying said desired duty cycle value before performing step d). 
     
     
       10. A method for controlling operation of an alternator comprising the steps of: a) using a controller to generate a pulse-width-modulated (PWM) signal having a specified duty cycle signal for energizing a field winding of said alternator;   b) setting a running sum value to zero;   c) using said controller to determine a desired duty cycle value for said PWM signal;   d) adding said desired duty cycle value to said running sum value;   e) using said controller to determine if said running sum value is greater than or equal to a first predetermined value;   f) if said running sum value is greater than or equal to said predetermined value, then causing said controller to turn "ON" said PWM signal to said field winding of said alternator for a predetermined time interval, and subtracting a second predetermined value from said running sum value;   g) if said running sum value is less than said first predetermined value, then causing said controller to turn "OFF" said PWM signal if said PWM signal is presently in a turned "ON" state, or to remain in a turned "OFF" state for said predetermined time interval; and   h) repeating steps c) through g).   
     
     
       11. The method of claim 10, wherein the first and second predetermined values are equal. 
     
     
       12. The method of claim 11, wherein said first and second predetermined values are each equal to 100. 
     
     
       13. The method of claim 10, wherein said first predetermined value is equal to 100. 
     
     
       14. The method of claim 10, further comprising the step of storing said running sum value in a memory associated with said controller after performing step d).